Excited states of 161Er deformed nucleus in the 161Tm decay

The paper is devoted to a detailed study of gammaray spectra delayed and nondelayed gamma-gamma coincidences, positrons and conversion electrons of 161Tm and to construction of the decay scheme of this nucleus. 161Tm isotope was produced in deep splitting of tantalum by 660-680 MeV protons in internal and external beams of the JINR synchrocyclotron. Conversion electrons were measured by β-spectrographs with a constant homogeneous magnetic field. The resolving power of spectrographs was 0.03-0.07%. Gamma-spectra were investigated by Ge(Li)-detectors. The spectrum of 161Tm positrons was measured by the Si(Li)-detector. The limiting energy of positrons was (1800+-100) keV. The results of measurements of spectra of gamma-rays and conversion electrons are shown in a table. 147 gamma transitions were observed. The results of studies of gamma-gamma coincidences are also tabulated. The scheme of decay 161Tm → 161Er was constructed basing on the results obtained and data of other papers. The estimation of population intensities of 161Er levels showed that β-decay of 161Tm proceeded mainly on the level with approximately 200 keV. The energy of decay 161Tm → 161Er was (3.0+-0.2) MeV. Values of lgft were calculated. A number of new levels and transitions were introduced. Multipolarities of some transition were first defined. Calculation was performed of the rotational spectrum of the band over isomeric state of 189.46 keV. A good agreement with the experiment was achieved